The present invention relates to an improvement in photosensitive imaging systems of the type taught in U.S. Pat. Nos. 4,399,209 and 4,440,846, wherein the photosensitive imaging system includes a protective coating.
Imaging systems employing microencapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. Nos. 4,399,209; 4,416,966; 4,440,846; 4,766,050; 5,783,353; 6,030,740; 6,037,094 and 6,080,520. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photohardenable composition in the internal phase is image-wise exposed to actinic radiation. In the most typical embodiments, the photohardenable composition is a photopolymerizable composition including a polyethylenically unsaturated compound and a photoinitiator and a color former is encapsulated with the photopolymerizable composition. Exposure to actinic radiation hardens the internal phase of the microcapsules. Following exposure, the imaging sheet is developed by subjecting it to a uniform rupturing force in the presence of a developer. An image transfer system in which the developer material is coated on a separate substrate as a separate developer or copy sheet is disclosed in commonly assigned U.S. Pat. No. 4,399,209. A self-contained imaging system in which the encapsulated color former and the developer material are present in one layer or in two interactive layers is disclosed in commonly assigned U.S. Pat. No. 4,440,846. Self-contained imaging systems having an opaque support are disclosed in commonly assigned U.S. Pat. No. 6,080,520. A two-sided imaging material is disclosed in commonly assigned U.S. Pat. No. 6,030,740.
U.S. Pat. No. 5,783,353, commonly assigned, discloses a self-contained imaging system wherein the imaging layer is sealed between two supports to form an integral unit. The sealed format is advantageous in that it can reduce oxygen permeation and improve stability of the media. Although the sealed format can improve media stability, some of the adhesives used between the imaging layer and the support can cause discoloration of the imaging layer.
In accordance with the present invention, a self-contained photosensitive material is provided which includes an imaging layer of photosensitive microcapsules and a developer on a support and a protective coating on the imaging layer. The protective coating, comprising a water-soluble or water-dispersible resin, provides scratch resistance and water resistance to the imaging media. The protective coating may also include a crosslinking agent.
In another embodiment of the invention, the self-contained photosensitive material includes a support, an imaging layer on the support and a protective coating on the imaging layer wherein the imaging layer comprises a layer of photosensitive microcapsules and a developer in the same or a separate layer as the microcapsules.
In a more particular embodiment of the invention, the protective coating comprises an acrylic latex and a polyaldehyde crosslinking agent.
In another embodiment of the present invention, an insolubilizer is present in at least one of the imaging layer and the protective coating. The insolubilizers as used in the present invention improve stability of the photosensitive material under various storage conditions. In particular, the insolubilizers improve humidity stability of the imaging media.